Wavelength Indication in Multiple-Wavelength Passive Optical Networks

ABSTRACT

An apparatus of a passive optical network (PON) comprising an optical line terminal (OLT) component configured to couple to an optical network unit (ONU) and send downstream wavelength identification to the ONU to indicate a wavelength that corresponds to the ONU, wherein the downstream wavelength identification is transmitted using a Media Access Control (MAC) layer frame for an embedded channel, a control message channel, or a data channel. Also included is an apparatus of a PON comprising an ONU component configured to couple to an OLT and send upstream wavelength feedback to the OLT to indicate a wavelength that corresponds to the ONU, wherein the upstream wavelength feedback is transmitted using a MAC layer frame for an embedded channel, a control message channel, or a data channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/473,439 filed Apr. 8, 2011 by Yuanqiu Luo, et al. andentitled “Wavelength Indication in Multiple-Wavelength Passive OpticalNetworks,” which is incorporated herein by reference as if reproduced inits entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

A passive optical network (PON) is one system for providing networkaccess over “the last mile.” The PON is a point to multi-point networkcomprised of an optical line terminal (OLT) at the central office, anoptical distribution network (ODN), and a plurality of optical networkunits (ONUs) at the customer premises. In some PON systems, such asGigabit PON (GPON) systems, downstream data is broadcasted at about 2.5gigabits per second (Gbps) while upstream data is transmitted at about1.25 Gbps. However, the bandwidth capability of the PON systems isexpected to increase as the demands for services increase. To meet theincreased demand in services, some emerging PON systems, such as NextGeneration Access (NGA) systems, are being reconfigured to transport thedata frames with improved reliability and efficiency at higherbandwidths, for example at about ten Gbps.

SUMMARY

In one embodiment, the disclosure includes an apparatus of a PONcomprising an OLT component configured to couple to an ONU and senddownstream wavelength identification to the ONU to indicate a wavelengththat corresponds to the ONU, wherein the downstream wavelengthidentification is transmitted using a Media Access Control (MAC) layerframe for an embedded channel, a control message channel, or a datachannel.

In another embodiment, the disclosure includes an apparatus of a PONcomprising an ONU component configured to couple to an OLT and sendupstream wavelength feedback to the OLT to indicate a wavelength thatcorresponds to the ONU, wherein the upstream wavelength feedback istransmitted using a MAC layer frame for an embedded channel, a controlmessage channel, or a data channel.

In another embodiment, the disclosure includes a method implemented atan OLT for a PON comprising sending, using a transmitter, a downstreamwavelength identification for an ONU that indicates a wavelength for theONU in a MAC layer frame for an embedded channel, a control messagechannel, or a data channel.

In yet another embodiment, the disclosure includes a method implementedat an ONU for a PON comprising sending, using a transmitter, an upstreamwavelength feedback for an OLT that indicates a wavelength for the ONUin a MAC layer frame for an embedded channel, a control message channel,or a data channel.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of a PON.

FIG. 2 is a schematic diagram of an embodiment of an embedded channelfor downstream wavelength identification.

FIG. 3 is a schematic diagram of another embodiment of an embeddedchannel for downstream wavelength identification.

FIG. 4 is a schematic diagram of another embodiment of an embeddedchannel for downstream wavelength identification.

FIG. 5 is a schematic diagram of an embodiment of a control messagechannel for downstream wavelength identification.

FIG. 6 is a schematic diagram of another embodiment of a control messagechannel for downstream wavelength identification.

FIG. 7 is a schematic diagram of another embodiment of a control messagechannel for downstream wavelength identification.

FIG. 8 is a schematic diagram of another embodiment of a control messagechannel for downstream wavelength identification.

FIG. 9 is a schematic diagram of another embodiment of a control messagechannel for downstream wavelength identification.

FIG. 10 is a schematic diagram of an embodiment of an embedded channelfor upstream wavelength feedback.

FIG. 11 is a schematic diagram of another embodiment of an embeddedchannel for upstream wavelength feedback.

FIG. 12 is a schematic diagram of an embodiment of a control messagechannel for upstream wavelength feedback.

FIG. 13 is a schematic diagram of another embodiment of a controlmessage channel for upstream wavelength feedback.

FIG. 14 is a schematic diagram of another embodiment of a controlmessage channel for upstream wavelength feedback.

FIG. 15 is a flowchart of an embodiment of a wavelengthidentification/feedback method.

FIG. 16 is a flowchart of another embodiment of a wavelengthidentification/feedback method.

FIG. 17 is a schematic diagram of an embodiment of an apparatusconfigured to implement a PON wavelength identification/feedback method.

FIG. 18 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

A plurality of systems that support higher bit rates and morewavelengths (or wavelength channels) have been proposed for nextgeneration PONs, such as a next generation PON (NGPON) architecture. Forexample, multiple-wavelength time division multiplexing (TDM) PONsystems may stack multiple GPONs or 10 GPONs (XGPONs) (e.g., about 4XGPONs) together using wavelength division multiplexing (WDM) technologyto achieve rates higher than about 10 Gbps (e.g., about 40 Gbps). OtherWDM-PON systems may connect different ONUs with different wavelengths inboth downstream (from the PON's OLT) transmissions and upstream (towardsthe OLT) transmissions. Further, some PON systems may be based onadvanced coding, modulation, and/or signal processing technologies, suchas orthogonal frequency division multiplexing (OFDM)-PONs and coherentWDM (CWDM)-PONs. Other examples include dynamic spectrum management-PON(DSM-PON) systems, where the system capacity is increased by improvingthe OLT intelligence to subgroup legacy GPON or XGPON ONUs.

Depending on the employed technologies, the multiple-wavelength-TDM PONsmay be classified as coarse WDM (CWDM)-TDM-PONs or dense WDM(DWDM)-TDM-PONs. Further, the WDM-PON may be splitter based or arrayedwaveguide grating (AWG) based. The OFDM-PON may also be extended into anOFDM-TDM-PON, an OFDM-WDM-PON, or an OFDM-WDM-TDM-PON. The PONs' ONUsmay be colorless, colored without wavelength tunability, colored withfull tunability, or colored with partial tunability. The trends above ofusing different types of PONs and ONUs may provide further enhancementfor GPON and XGPON bandwidth, e.g., to obtain a NGPON system that servesa larger number of ONUs/ONTs at longer distances.

The trends and enhancements above may be used for existing protocols ofGPON, XGPON, Ethernet PON (EPON), and 10 gigabit EPON (10GEPON) systems,which may be originally designed for TDM/TDM access (TDMA) management.The systems resulting from using these trends and enhancements may havemultiple-wavelength capability and use a suitable management mechanismto manage the different wavelengths (or wavelength channels).

Disclosed herein is a system and methods for supportingmultiple-wavelength capability in PONs. The system and methods mayenable wavelength indication in the multiple-wavelength PON. The methodsmay comprise mechanisms for downstream wavelength identification andupstream wavelength feedback. The downstream wavelength identificationmay be used in the case where the PON's ONU receives a single wavelength(or wavelength channel), and thus the ONU may need to know whichwavelength the ONU is assigned (by the PON's OLT). Identifying theassigned wavelength to the corresponding ONU may enable the ONU toconfigure or align its receiver (or filter) to properly receive theassociated wavelength channel. The ONU may obtain this information byreceiving an identifying protocol element for each assigned downstreamwavelength. The wavelength indication may be sent in a MAC layer frameor message. The upstream wavelength feedback may be needed in the casewhere the OLT needs to associate the upstream transmissions from the ONUwith the downstream wavelength which the ONU is receiving. Thus, the OLTmay be able to separate or distinguish the downstream and associatedupstream wavelength channels for each ONU. By feeding back a wavelengthidentifier (ID) upstream to the OLT, the OLT may be able to make thisassociation. The methods of wavelength identification may be implementedfor GPON, XGPON, EPON, and 10GEPON protocols, for example, or for anyother PON protocols that may support wavelength labeling.

FIG. 1 illustrates one embodiment of a PON 100. The PON 100 may comprisean OLT 110, a plurality of ONUs 120, and an ODN 130, which may becoupled to the OLT 110 and the ONUs 120. The PON 100 may be acommunications network that does not require any active components todistribute data between the OLT 110 and the ONUs 120. Instead, the PON100 may use the passive optical components in the ODN 130 to distributedata between the OLT 110 and the ONUs 120. The PON 100 may be NGAsystems, such as XGPONs, which may have a downstream bandwidth of aboutten Gbps and an upstream bandwidth of at least about 2.5 Gbps. Otherexamples of suitable PONs 100 include the asynchronous transfer mode PON(APON) and the broadband PON (BPON) defined by the InternationalTelecommunication Union Telecommunication Standardization Sector (ITU-T)G.983 standard, the GPON defined by the ITU-T G.984 standard, the EPONdefined by the Institute of Electrical and Electronics Engineers (IEEE)802.3ah standard, the 10GEPON as described in the IEEE 802.3av standard,and the Wavelength Division Multiplexed WDM-PON. Additionally, the PON100 may also have multiple-wavelength capability, where multipledownstream and/or upstream wavelengths (or wavelength channels) may beused to carry data, such as for different ONUs 120 or customers.Accordingly, the PON protocol may be configured to support any of themultiple-wavelength technologies described above.

The OLT 110 may be any device that is configured to communicate with theONUs 120 and another network (not shown). The OLT 110 may act as anintermediary between the other network and the ONUs 120. For instance,the OLT 110 may forward data received from the network to the ONUs 120,and forward data received from the ONUs 120 onto the other network.Although the specific configuration of the OLT 110 may vary depending onthe type of PON 100, in an embodiment, the OLT 110 may comprise atransmitter and a receiver. When the other network is using a networkprotocol, such as Ethernet or Synchronous Optical Networking(SONET)/Synchronous Digital Hierarchy (SDH), that is different from thePON protocol used in the PON 100, the OLT 110 may comprise a converterthat converts the network protocol into the PON protocol. The OLT 110converter may also convert the PON protocol into the network protocol.The OLT 110 may be typically located at a central location, such as acentral office, but may be located at other locations as well.

The ONUs 120 may be any devices that are configured to communicate withthe OLT 110 and a customer or user (not shown). The ONUs 120 may act asan intermediary between the OLT 110 and the customer. For instance, theONUs 120 may forward data received from the OLT 110 to the customer, andforward data received from the customer onto the OLT 110. Although thespecific configuration of the ONUs 120 may vary depending on the type ofPON 100, in an embodiment, the ONUs 120 may comprise an opticaltransmitter configured to send optical signals to the OLT 110 and anoptical receiver configured to receive optical signals from the OLT 110.The transmitters and receivers at different ONUs 120 may use differentwavelengths to transmit and receive optical signals that carry data. Thetransmitter and receiver at the same ONU 120 may use the same wavelengthor different wavelengths. Additionally, the ONUs 120 may comprise aconverter that converts the optical signal into electrical signals forthe customer, such as signals in the Ethernet protocol, and a secondtransmitter and/or receiver that may send and/or receive the electricalsignals to a customer device. In some embodiments, ONUs 120 and opticalnetwork terminals (ONTs) are similar, and thus the terms are usedinterchangeably herein. The ONUs may be typically located at distributedlocations, such as the customer premises, but may be located at otherlocations as well.

The ODN 130 may be a data distribution system, which may compriseoptical fiber cables, couplers, splitters, distributors, and/or otherequipment. The optical fiber cables, couplers, splitters, distributors,and/or other equipment may be passive optical components that may notrequire any power to distribute data signals between the OLT 110 and theONUs 120. Alternatively, the ODN 130 may comprise one or a plurality ofprocessing equipment, such as optical amplifiers. The ODN 130 maytypically extend from the OLT 110 to the ONUs 120 in a branchingconfiguration as shown in FIG. 1, but may be alternatively configured inany other point-to-multi-point configuration.

To support multiple-wavelength capability, the PON 100 may comprise oneor more AWGs, such as at the ODN 130 and/or the OLT 110. The AWGs may beconfigured to combine/split multiple wavelength channels, which may beoptical signals transmitted at different wavelengths, in theupstream/downstream directions. The PON 100 may also be configured toimplement one or more methods for wavelength identification to indicateto the ONUs 120 and/or the OLT 110 which wavelengths (or wavelengthchannels) are assigned to the corresponding ONUs 120. The wavelengthidentification methods may be used to indicate the wavelengths to theONUs 120, to the OLT 110, or both. The wavelength identification methodsmay be used to identify the wavelengths for downstream data channels(form the OLT 110 to the ONUs 120), upstream data channels (from theONUs 120 to the OLT 110), or both. The wavelength identification methodsmay comprise downstream wavelength identification mechanisms andupstream wavelength feedback mechanisms as described below.

Downstream wavelength identification may be used to identify thewavelengths for downstream transmission to the ONUs. Downstreamwavelength identification may be established using different mechanismsor implementations, which may be used to send a downstream wavelengthidentification (e.g., from the OLT 110 to a corresponding ONU 120). Thedifferent mechanisms may use MAC layer frames or messages to carry thewavelength identification. A first mechanism for downstream wavelengthidentification may use an embedded channel. The embedded channelmechanism or approach may use in-band frame fields and embeddedstructures to carry low-level operations, administration, and management(OAM) information. The embedded channel may typically offer alow-latency path for fast actions and enable basic functions for MACdevises. Examples of the embedded channels include the embedded OAM inGPON and XGPON protocols, and the logical link identifier (LLID) in EPONand 10GEPON protocols.

A second mechanism for downstream wavelength identification may use acontrol message channel. The control message channel may employ protocolmanagement messages to facilitate the connections between the OLT andthe ONUs. Examples of the control message channel include a physicallayer OAM (PLOAM) message in GPON and XGPON protocols, and a multi-pointcontrol protocol (MPCP) message in EPON and 10GEPON protocols. A thirdmechanism for downstream wavelength identification may use a datachannel. Specifically, the wavelength information may be carried in thePON data channel to the ONUs. In GPON and XGPON protocols, GPONencapsulation method (GEM) or 10 GEM (XGEM) ports may be configured byan ONT management and control interface (OMCI) for this purpose. In EPONand 10GEPON protocols, the LLIDs may be designed towards this end.

FIG. 2 illustrates an embodiment of a portion of a frame or message 200corresponding to an embedded channel that may be used for downstreamwavelength identification. The embedded channel may be an embedded OAMchannel for the GPON protocol and may use a portion of a GPON downstreamframe. The GPON embedded OAM channel information may be sent from theOLT to a corresponding ONU for downstream wavelength identification. TheOLT may use the GPON downstream frame to indicate to the ONU theassigned wavelength for downstream transmissions. The downstreamwavelength identification may be sent in a GPON downstream frame thatcomprises a Payload Length downstream (Plend) field 210. The Plend field210 may include a B length (Blen) subfield 212, an A length (Alen)subfield 214, and a cyclic redundancy check (CRC) subfield 216. ThePlend field 210 may have a total size of about 32 bits. The Blensubfield 212 may indicate the length (in bytes) of another field (notshown) in the message or frame. The Blen subfield 212 may have a size ofabout 12 bits. The Alen subfield 214 may indicate the downstreamwavelength. The Alen subfield 214 may have a size of about 12 bits. TheCRC subfield 216 may have a size of about 8 bits and may be configuredas defined in the GPON protocol.

FIG. 3 illustrates an embodiment of another frame or message portion 300corresponding to an embedded channel 300 that may be used for downstreamwavelength identification. The embedded channel may be an embedded OAMchannel for the XGPON protocol and may use a portion of an XGPONdownstream Physical layer (PHY) frame. The XGPON downstream PHY framemay comprise a 24-byte physical synchronization block (PSBd) and a155496-byte PHY frame payload. The PSBd may comprise a PON-ID structure310, which may be used to indicate the downstream wavelength (from theOLT to the corresponding ONU). The PON-ID structure 310 may have a sizeof about 64 bits. The PON-ID structure 310 may comprise a PON-ID field320 and a header error control (HEC) field 330. The PON-ID field 320 maycomprise an assigned PON-ID subfield 322 and a wavelength ID subfield324. The PON-ID subfield 322 may indicate a PON ID for a correspondingONU and the wavelength ID subfield 324 may indicate the downstreamwavelength for the ONU. The PON-ID field 320 may have a size of about 51bits, the assigned PON-ID subfield 322 may have a size of about 51-xbits, where x is an integer, and the wavelength ID subfield 324 may havea size of about x bits. The HEC field 330 may have a size of about 13bits and may be configured as defined in the XGPON protocol. The integerx may be determined based on the number of downstream wavelengths in themultiple-wavelength PON system. Typical values of x may be equal to 4,5, or 6 to represent 16, 32, or 64 total downstream wavelengths,respectively. The actual order of the assigned PON-ID subfield 322 andthe wavelength ID subfield 324 may be similar or different than theorder shown in FIG. 3.

Since the GPON and XGPON downstream frames may be broadcasted from theOLT to a plurality of or all the ONUs, e.g., with a lifetime or durationof about 125 microsecond (μs), the wavelength ID may be announced to theONUs for the same downstream wavelength periodically. The ONUs may beconfigured to confirm the downstream wavelength by comparing thewavelength ID and the corresponding ONUs' receiver wavelengths.

FIG. 4 illustrates an embodiment of another embedded channel 400 fordownstream wavelength identification. The embedded channel 400 may be anembedded LLID channel for EPON or 10GEPON protocols and may use aportion of an EPON downstream frame. In EPON and 10GEPON, the LLID maybe assigned to a point-to-multi-point (P2MP) association between an OLTand multiple ONUs, where each ONU association may be established througha point-to-point (P2P) emulation. The EPON downstream frame may comprisean LLID field 410. The LLID field 410 may comprise a mode subfield 412,an assigned LLID subfield 414, and a wavelength ID subfield 416. TheLLID field 410 may have a size of about 16 bits. The mode subfield 412may be a one bit flag that is set to indicate the assigned LLID. Themode subfield 412 may correspond to the most significant bit (MSB) inthe LLID field 410. The assigned LLID subfield 414 may indicate the LLIDassigned for a corresponding ONU. The assigned LLID subfield 414 mayhave a size of about 15-y bits, where y is an integer. The wavelength IDsubfield 416 may indicate the downstream wavelength for the ONU. Thewavelength ID subfield 416 may have a size of about y bits. The actualorder of the wavelength ID subfield 416 may be similar or different thanthe order shown in FIG. 4.

In the control message channel mechanism or approach for downstreamwavelength identification, a PLOAM channel message may be used in GPONand XGPON protocols. The downstream wavelength identification may beimplemented using a new PLOAM message or a modified PLOAM message, asdescribed below. FIG. 5 illustrates an embodiment of a control messagechannel 500 for downstream wavelength identification. The controlmessage channel 500 may use a modified upstream overhead PLOAM messagefor the GPON protocol. The modified upstream overhead PLOAM message maycomprise about 12 fields, which may each have a size of about one octet.The fields of the upstream overhead PLOAM message shown in FIG. 5 may beconfigured as defined in the GPON protocol. However, some of the fieldsor bits may be modified to enable downstream wavelength identification.Specifically, the bits in octets 3 to 5 may not be fully used torepresent the bit numbers in the corresponding fields (guard bit number,type 1 preamble bit number, and type 2 preamble bit number). Such bitsin the corresponding octets (or fields) may be used for downstreamwavelength identification. Additionally, some of the bits in octet 10(for various indication) may also be used for downstream wavelengthidentification. The octets that may be at least partially used for thispurpose are shaded in FIG. 5.

FIG. 6 illustrates an embodiment of another control message channel 600for downstream wavelength identification. The control message channel600 may use a modified upstream profile PLOAM message for the XGPONprotocol. The modified profile PLOAM message may comprise about 13fields, which may have a total size of about 48 octets. The fields andcorresponding sizes shown in FIG. 6 may be configured as defined in theXGPON protocol. However, some of the fields are modified to enabledownstream wavelength identification. Specifically, the bits in octets 5to 7, 16 to 17, and 34 to 40 may not be fully used in the correspondingfields. At least some of the bits in octets 5 to 7 (for profile versionand index, forward error correction (FEC) indication, and delimiterlength), some of the bits in octets 16 to 17 (for preamble length andpreamble repeat count), and/or some of the bits in octets 34 to 40 (forpadding) may be used for downstream wavelength identification. Theoctets that may be at least partially used for this purpose are shadedin FIG. 6.

FIG. 7 illustrates an embodiment of another control message channel 700for downstream wavelength identification. The control message channel700 may be a new PLOAM message for the XGPON and GPON protocols. The newPLOAM message may comprise about 6 fields, which may have a total sizeof about 48 octets. The fields and corresponding sizes are shown in FIG.7. Specifically, a downstream wavelength field may be used to indicatethe downstream wavelength. The downstream wavelength field may use octet5 to “a”, where “a” is an integer.

FIG. 8 illustrates an embodiment of another control message channel 800for downstream wavelength identification. The control message channel800 may use a modified gate MPCP data unit (MPCPDU) for the EPON and10GEPON protocols. The MPCPDUs are Ethernet frames that carrymulti-point MAC control information. The modified gate MPCPDU maycomprise about 8 fields, which may have a total size of about 64 octets.The fields and corresponding sizes shown in FIG. 8 may be configured asdefined in the EPON and 10GEPON protocols. However, some of the fieldsare modified to enable downstream wavelength identification.Specifically, the bits in octets 22 to 60 may not be fully used (forgrant and pad). Some of the bits in octets 22 to 66 may be used fordownstream wavelength identification. The octets that may be at leastpartially used for this purpose are shaded in FIG. 8.

FIG. 9 illustrates an embodiment of another control message channel 900for downstream wavelength identification. The control message channel900 may be a new MPCPDU for the EPON and 10GEPON. The new MPCPDU maycomprise about 8 fields, which may have a total size of about 64 octets.The fields and corresponding sizes are shown in FIG. 9. Specifically, adownstream wavelength field may be used to indicate the downstreamwavelength. The downstream wavelength field may use octets 21 to “b”octets, where “b” is an integer.

In the data channel mechanism or approach for downstream wavelengthidentification, a user data channel (data message) may be configured todeliver the downstream wavelength information in the GPON and XGPONprotocols. Similar to providing multicast services, an OMCI may be usedto configure GEM or XGEM ports to send this information. In the EPON and10GEPON protocols, a broadcast LLID may be defined for this purpose. Theframes that comprise the broadcast LLID may also include content fordownstream wavelength identification.

FIG. 10 illustrates an embodiment of an embedded channel 1000 forupstream wavelength feedback. The embedded channel 1000 may be anembedded OAM channel for the GPON protocol and may use a GPON upstreamburst header. This GPON embedded OAM channel information may be sentfrom the ONU to the OLT for upstream wavelength feedback. The ONU mayuse the GPON upstream burst header to indicate to the OLT the wavelengthfor upstream transmissions or for the ONU's receiver. The upstreamwavelength feedback may be sent in a GPON upstream burst header thatcomprises an indication (Ind) field 1010. The Ind field 1010 may includean urgent PLOAM units subfield 1012, a FEC subfield 1014, a remotedefect indication (RDI) subfield 1016, a wavelength ID subfield 1018,and a reserved subfield 1020. The subfields may be configured as definedin the GPON protocol, where the MSB reports urgent PLOAM and thefollowing two bits report FEC and RDI status respectively. However,about z bits from the 5 currently reserved bits may be used to indicatethe upstream wavelength, where z is an integer. The remaining 5-z bitsmay remain reserved. The actual order of the wavelength ID subfield 1018may be similar or different than the order shown in FIG. 10. Using thewavelength ID in the GPON upstream burst header, the OLT may be able toconfirm or check the wavelength of an ONU in the protocol layer.

FIG. 11 illustrates an embodiment of another embedded channel 1100 forupstream wavelength feedback. The embedded channel 1100 may be anembedded OAM channel for the XGPON protocol and may use a XGPONTransmission Container (XGTC) burst header. The XGPON embedded OAMchannel information may be sent from the ONU to the OLT for upstreamwavelength feedback. The ONU may use the XGTC burst header to indicateto the OLT the wavelength for upstream transmissions. The upstreamwavelength feedback may be sent in a XGTC burst header 1110 thatcomprises an ONU-ID field 1120, and Ind field 1130, a HEC field 1140,and a PLOAM unit field 1150, which may be configured as defined in theXGPON protocol. The ONU-ID field 1120 may have a size of about 10 bits.The Ind field 1130 may have a size of about 9 bits. The HEC field 1140may have a size of about 13 bits. The PLOAM unit field 1150 may beoptional and may have a size up to about 384 bits. The ONU-ID field 1120may comprise a PLOAM queue status subfield 1122 that may be the MSB (aone bit flag), a reserved subfield 1124, a wavelength ID subfield 1126,and a dying gasp subfield 1128 that may be the least significant bit(LSB). About n bits from the 7 currently reserved bits may be used toindicate the upstream wavelength, where n is an integer. The remaining7-n bits may remain reserved. The integer n may be determined based onthe number of wavelengths in the multiple-wavelength PON system. Typicalvalues of n may be are 4, 5, or 6 to represent 16, 32, or 64 totalwavelengths respectively. The actual order of the wavelength ID subfield1126 may be similar or different than the order shown in FIG. 10.

In another embodiment, upstream wavelength feedback may be achieved bydefining different delimiters for different downstream wavelengths.Thus, multiple ONUs that share the same downstream wavelength may usethe same type of delimiter. For example, delimiter type 1 may be fordownstream wavelength 1 and delimiter type 2 may be for downstreamwavelength 2. As such, the upstream burst delimiter may indicate to theOLT the working downstream wavelength of the corresponding ONU. In someembodiments for EPONs and 10GEPONs, a 2-byte LLID may be modified asshown in FIG. 4 to support upstream wavelength feedback. Accordingly,some bits may be assigned to carry the feedback. After receiving thisinformation, the OLT may be able to correlate the downstream andupstream wavelengths for an ONU.

FIG. 12 illustrates an embodiment of a control message channel 1200 forupstream wavelength feedback. The control message channel 1200 may be anew PLOAM message for the XGPON and GPON protocols. The new PLOAMmessage may comprise about 6 fields, which may have a total size ofabout 48 octets. The fields and corresponding sizes are shown in FIG.12. Specifically, a wavelength field may be used to indicate theupstream wavelength feedback. The wavelength field may use octet 5 to“a”, where “a” is an integer.

Similar to the control message channels 500 and 600 for downstreamwavelength identification that use modified PLOAM messages for GPON andXGPON respectively, control message channels that use modified PLOAMmessages may also be used for upstream wavelength feedback for the GPONand XGPON protocols. For example, in the GPON protocol, an acknowledgePLOAM message or a No PLOAM message may be modified. A Serial_Number_ONUfield in the PLOAM message may be modified to carry the upstreamwavelength feedback. Similarly, in the XGPON protocol, an acknowledgePLOAM message and a Serial_Number_ONU PLOAM field in the message may bemodified to carry the wavelength feedback.

FIG. 13 illustrates an embodiment of another control message channel1300 for upstream wavelength feedback. The control message channel 1300may use a modified report MPCPDU for the EPON and 10GEPON protocols. Themodified report MPCPDU may comprise about 8 fields, which may have atotal size of about 64 octets. The fields and corresponding sizes shownin FIG. 13 may be configured as defined in the EPON and 10GEPONprotocols. However, some of the fields are modified to enable upstreamwavelength feedback. Specifically, the bits in octets 23 to 60 may notbe fully used (for report and pad). Some of the bits in octets 23 to 60may be used for upstream wavelength feedback. The octets that may be atleast partially used for this purpose are shaded in FIG. 13.

FIG. 14 illustrates an embodiment of another control message channel1400 for upstream wavelength feedback. The control message channel 1400may be a new MPCPDU for the EPON and 10GEPON. The new MPCPDU maycomprise about 8 fields, which may have a total size of about 64 octets.The fields and corresponding sizes are shown in FIG. 14. Specifically, awavelength field may be used to indicate the wavelength feedback. Thewavelength field may use octets 21 to “b” octets, where “b” is aninteger.

In the data channel approach for upstream wavelength feedback, a userdata channel (data message) may be configured to deliver the wavelengthfeedback in the GPON and XGPON protocols. GEM or XGEM ports may beconfigured by OMCI for this purpose. In the EPON and 10GEPON protocols,a dedicated or special LLID may be defined for this purpose. The framesthat comprise the dedicated LLID may also include content for wavelengthfeedback.

In other embodiments, the upstream wavelength feedback may indicate theactual wavelength being used for the upstream transmission (instead ofthe wavelength or channel ID). The OLT equipment may typically know thisinformation based on which receiver channel the transmission arrives onfrom the ONUs. However, the actual wavelength information from the ONUsmay be used as a double check. The wavelength information exchangedbetween the OLT and its associated ONUs may be absolute values, relativevalues, or identification values (e.g., IDs). The relative value may berelevant to a previous exchanged value or a pre-determined absolutebenchmark value. In order to support identification values, a certainmechanism of wavelength profiling may be used. Different schemes may beused to define the specific mapping between wavelengths and their IDs.For example, some PLOAM messages (e.g., profile PLAOM message) may beextended to carry such information. Alternatively, new control messagesmay be defined for this purpose.

FIG. 15 illustrates an embodiment of a wavelengthidentification/feedback method 1500, which may be implemented in amultiple-wavelength PON system to exchange wavelength informationbetween an OLT and a corresponding ONU. The method 1500 may begin atblock 1510, where a downstream wavelength identification may be sent.The OLT may send the downstream wavelength identification to thecorresponding ONU using any of the mechanisms or approaches and theappropriate corresponding messages for downstream wavelengthidentification described above, e.g., based on the PON protocol. Theapproaches include the embedded channels 200, 300, and 400, the controlmessage channels 500, 600, 700, 800, and the data channels fordownstream wavelength identification. As such, the OLT may identify thewavelength for the corresponding ONU. The wavelength identified may bethe wavelength used to send data to that ONU. At block 1520, an upstreamwavelength feedback may be received. The OLT may receive the upstreamwavelength feedback from the corresponding ONU using an approach,channel, or message similar or corresponding to the one used for sendingthe downstream wavelength identification, e.g., based on the same PONprotocol. The approaches include the embedded channels 1000 and 11000,the control message channels 1200, 1300, and 1400, and the data channelsfor upstream wavelength feedback. As such, the ONU may confirm or informthe OLT of the actual wavelength that is used at the ONU to receivedata. The method 1500 may then end.

The method 1500 may be used to confirm the wavelengths used by the ONUs,to inform the OLT of the wavelengths used by the ONUs, to change thewavelengths used by the ONUs, or to correct or synchronize thewavelength usage information. In other embodiments, the block 1510 or1520 may be implemented separately and independently withoutimplementing the other block to convey the wavelength information in thedownstream or upstream direction. Although the method 1500 is describedin terms of the wavelengths used at the ONUs' receivers. A similarmethod may be used for the wavelengths used at the ONUs' transmitters orboth at the ONUs' receivers and transmitters.

FIG. 16 illustrates another embodiment of a wavelengthidentification/feedback method 1600, which may be implemented in amultiple-wavelength PON system to exchange wavelength informationbetween an ONU and an OLT. The method 1600 may begin at block 1610,where a downstream wavelength identification may be received. The ONUmay receive the downstream wavelength identification from the OLT usingany of the approaches and the appropriate corresponding messages fordownstream wavelength identification described above, e.g., based on thePON protocol. The wavelength identified may be the wavelength used bythe OLT to send data to the ONU. At block 1620, an upstream wavelengthfeedback may be sent. The ONU may send the upstream wavelength feedbackto the OLT using a corresponding approach, channel, or message to theone used for sending the downstream wavelength identification, e.g.,based on the same PON protocol. As such, the ONU may confirm or informthe OLT of the actual wavelength that is used at the ONU to receivedata. The method 1600 may then end.

The method 1600 may be used to confirm the wavelengths used by the ONUs,to inform the OLT of the wavelengths used by the ONUs, to change thewavelengths used by the ONUs, or to correct or synchronize thewavelength usage information. In other embodiments, the block 1610 or1620 may be implemented separately and independently withoutimplementing the other block to convey the wavelength information in thedownstream or upstream direction. The method 1600 may be used foridentifying/acknowledging the wavelengths used at the ONUs' receivers,at the ONUs' transmitters, or both.

FIG. 17 illustrates an embodiment of an apparatus 1700 that may beconfigured to support and implement the wavelengthidentification/feedback method 1500 or 1600. The apparatus 1700 maycomprise a processing unit 1710, a transmission unit (or transmitter)1720, and a reception unit (or receiver) 1730 that may be configured toimplement the method 1500 or 1600. For example, the apparatus 1700 maybe located at an OLT and may implement the method 1500. Alternatively,the apparatus 1700 may be located at an ONU and may be configured toimplement the method 1600. The processing unit 1710, the transmissionunit 1720, and the reception unit 1730 may correspond to hardware,firmware, and/or software installed to run hardware. The processing unit1710 may be configured to put or get the wavelength ID (or value) fordownstream wavelength identification or upstream wavelength feedback ina MAC layer based frame or message, e.g., that corresponds to anembedded channel, a control message channel, or a data channel. Theprocessing unit 1710 may send or receive the MAC layer based message orframe comprising the wavelength identification/feedback to thetransmission unit 1720 or from the reception unit 1730, respectively.The transmission unit or transmitter 1720 may be configured to transmitthe message or frame (at the MAC layer), and the reception unit orreceiver 1730 may be configured to receive the message or frame. At theOLT, the transmission unit 1720 may send a frame for downstreamwavelength identification and the reception unit 1730 may receive aframe for upstream wavelength feedback. At the ONU, the reception unit1730 may receive a frame for downstream wavelength identifications andthe transmission unit 1720 may send a frame for upstream wavelengthfeedback.

The components, methods, and mechanisms described above may beimplemented on any general-purpose network component (at the OLT orONU), such as a computer or network component with sufficient processingpower, memory resources, and network throughput capability to handle thenecessary workload placed upon it. FIG. 18 illustrates a typical,general-purpose network component 1800 suitable for implementing one ormore embodiments of the components, methods, and mechanisms disclosedherein. The network component 1800 includes a processor 1802 (which maybe referred to as a central processor unit or CPU) that is incommunication with memory devices including secondary storage 1804, readonly memory (ROM) 1806, random access memory (RAM) 1808, input/output(I/O) devices 1810, and network connectivity devices 1812. The processor1802 may be implemented as one or more CPU chips, or may be part of oneor more application specific integrated circuits (ASICs).

The secondary storage 1804 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 1808 is not large enough tohold all working data. Secondary storage 1804 may be used to storeprograms that are loaded into RAM 1808 when such programs are selectedfor execution. The ROM 1806 is used to store instructions and perhapsdata that are read during program execution. ROM 1806 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage 1804. The RAM 1808 is usedto store volatile data and perhaps to store instructions. Access to bothROM 1806 and RAM 1808 is typically faster than to secondary storage1804.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upperlimit, R_(u), is disclosed, any number falling within the range isspecifically disclosed. In particular, the following numbers within therange are specifically disclosed: R=R₁+k*(R_(u)−R_(l)), wherein k is avariable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 7percent, . . . , 70 percent, 71 percent, 72 percent, . . . , 97 percent,96 percent, 97 percent, 98 percent, 99 percent, or 100 percent.Moreover, any numerical range defined by two R numbers as defined in theabove is also specifically disclosed. Use of the term “optionally” withrespect to any element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as comprises,includes, and having should be understood to provide support fornarrower terms such as consisting of, consisting essentially of, andcomprised substantially of. Accordingly, the scope of protection is notlimited by the description set out above but is defined by the claimsthat follow, that scope including all equivalents of the subject matterof the claims. Each and every claim is incorporated as furtherdisclosure into the specification and the claims are embodiment(s) ofthe present disclosure. The discussion of a reference in the disclosureis not an admission that it is prior art, especially any reference thathas a publication date after the priority date of this application. Thedisclosure of all patents, patent applications, and publications citedin the disclosure are hereby incorporated by reference, to the extentthat they provide exemplary, procedural, or other details supplementaryto the disclosure.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. An apparatus of a passive optical network (PON)comprising: an optical line terminal (OLT) component configured tocouple to an optical network unit (ONU) and send downstream wavelengthidentification to the ONU to indicate a wavelength that corresponds tothe ONU, wherein the downstream wavelength identification is transmittedusing a Media Access Control (MAC) layer frame for an embedded channel,a control message channel, or a data channel.
 2. The apparatus of claim1, wherein the OLT component is further configured to receive upstreamwavelength feedback from the ONU that indicates a wavelength thatcorresponds to the ONU, and wherein the upstream wavelength feedback istransmitted using a second MAC layer frame.
 3. The apparatus of claim 2,wherein the downstream wavelength identification is sent when the ONU isassigned a determined downstream wavelength channel and needs to knowwhich downstream wavelength channel is assigned to the ONU, and whereinthe upstream wavelength feedback is sent to allow the OLT to associateupstream transmissions from the ONU with the determined downstreamwavelength channel.
 4. The apparatus of claim 1, wherein the MAC layerframe is a gigabit PON (GPON) downstream frame for an embeddedoperations, administration, and management (OAM) channel that comprisesa payload length (Plend) field, and wherein the Plend field includes awavelength identifier (ID) that indicates the wavelength for the ONU. 5.The apparatus of claim 1, wherein the MAC layer frame is a 10 gigabitPON (XGPON) downstream Physical Layer (PHY) frame for an embeddedoperations, administration, and management (OAM) channel that comprisesa PON identifier (ID) field, and wherein the PON ID field includes awavelength ID that indicates the wavelength for the ONU.
 6. Theapparatus of claim 1, wherein the MAC layer frame is an Ethernet PON(EPON) or 10 gigabit EPON (10GEPON) downstream frame for an embeddedlogical link identifier (LLID) channel that comprises a LLID field, andwherein the LLID field includes a wavelength identifier (ID) thatindicates the wavelength for the ONU.
 7. The apparatus of claim 1,wherein the MAC layer frame is a modified gigabit PON (GPON) PLOAMmessage for an embedded control channel that comprises a plurality ofoctets for bit numbers and various indication, and wherein some of thebits in the octets are used to indicate the wavelength for the ONU. 8.The apparatus of claim 1, wherein the MAC layer frame is a modified 10gigabit PON (XGPON) PLOAM message for an embedded control channel thatcomprises a plurality of octets for profile version and index, forwarderror correction (FEC), and delimiter length, and wherein some of thebits in the octets are used to indicate the wavelength for the ONU. 9.The apparatus of claim 1, wherein the MAC layer frame is a new gigabitPON (GPON) or 10 GPON (XGPON) PLOAM message for an embedded controlchannel that comprises a plurality of octets, and wherein some of theoctets are used to indicate the wavelength for the ONU.
 10. Theapparatus of claim 1, wherein the MAC layer frame is a modified EthernetPON (EPON) or 10 gigabit EPON (10GEPON) multi-point control protocoldata unit (MPCPDU) for an embedded control channel that comprises aplurality of octets for grant and pad, and wherein some of the bits inthe octets are used to indicate the wavelength for the ONU.
 11. Theapparatus of claim 1, wherein the MAC layer frame is a new Ethernet PON(EPON) or 10 gigabit EPON (10GEPON) multi-point control protocol dataunit (MPCPDU) for an embedded control channel that comprises a pluralityof octets, and wherein some of the octets are used to indicate thewavelength for the ONU.
 12. The apparatus of claim 1, wherein the MAClayer frame is a gigabit PON (GPON) or 10 GPON (XGPON) message for auser data channel that indicates the wavelength for the ONU, and whereina GPON encapsulation method (GEM) or 10 GEM (XGEM) port is configuredusing an ONT management and control interface (OMCI) for downstreamwavelength identification.
 13. The apparatus of claim 1, wherein the MAClayer frame is an Ethernet PON (EPON) or 10 gigabit EPON (10GEPON)message for a user data channel that indicates the wavelength for theONU, and wherein the EPON or 10GEPON message includes a broadcastlogical link identifier (LLID) configured for downstream wavelengthidentification.
 14. An apparatus of a passive optical network (PON)comprising: an optical network unit (ONU) component configured to coupleto an optical line terminal (OLT) and send upstream wavelength feedbackto the OLT to indicate a wavelength that corresponds to the ONU, whereinthe upstream wavelength feedback is transmitted using a Media AccessControl (MAC) layer frame for an embedded channel, a control messagechannel, or a data channel.
 15. The apparatus of claim 14, wherein theONU component is further configured to receive downstream wavelengthidentification from the OLT that indicates a wavelength that correspondsto the ONU, and wherein the downstream wavelength identification istransmitted using a second MAC layer frame.
 16. The apparatus of claim14, wherein the MAC layer frame is a gigabit PON (GPON) upstream burstheader for an embedded operations, administration, and management (OAM)channel that comprises an indication (Ind) field, and wherein the Indfield includes a wavelength identifier (ID) that indicates thewavelength for the ONU.
 17. The apparatus of claim 14, wherein the MAClayer frame is a 10 gigabit PON (XGPON) transmission container (XGTC)burst header for an embedded operations, administration, and management(OAM) channel that comprises an ONU identifier (ID) field, and whereinthe ONU ID field includes a wavelength ID that indicates the wavelengthfor the ONU.
 18. The apparatus of claim 14, wherein the MAC layer frameis an Ethernet PON (EPON) or 10 gigabit EPON (10GEPON) upstream framefor an embedded logical link identifier (LLID) channel that comprises aLLID field, and wherein the LLID field includes a wavelength identifier(ID) that indicates the wavelength for the ONU.
 19. The apparatus ofclaim 14, wherein the MAC layer frame is a new gigabit PON (GPON) or 10GPON (XGPON) PLOAM message for an embedded control channel thatcomprises a plurality of octets, and wherein some of the octets are usedto indicate the wavelength for the ONU.
 20. The apparatus of claim 14,wherein the MAC layer frame is a modified gigabit PON (GPON) or 10gigabit PON (XGPON) acknowledge PLOAM message for an embedded controlchannel that comprises a modified Serial_Number_ONU field to indicatethe wavelength for the ONU.
 21. The apparatus of claim 14, wherein theMAC layer frame is a modified Ethernet PON (EPON) or 10 gigabit EPON(10GEPON) multi-point control protocol data unit (MPCPDU) for anembedded control channel that comprises a plurality of octets for reportand pad, and wherein some of the bits in the octets are used to indicatethe wavelength for the ONU.
 22. The apparatus of claim 14, wherein theMAC layer frame is a new Ethernet PON (EPON) or 10 gigabit EPON(10GEPON) multi-point control protocol data unit (MPCPDU) for anembedded control channel that comprises a plurality of octets, andwherein some of the octets are used to indicate the wavelength for theONU.
 23. The apparatus of claim 14, wherein the MAC layer frame is agigabit PON (GPON) or 10 GPON (XGPON) message for a user data channelthat indicates the wavelength for the ONU, and wherein a GPONencapsulation method (GEM) or 10 GEM (XGEM) port is configured using anONT management and control interface (OMCI) for upstream wavelengthfeedback.
 24. The apparatus of claim 14, wherein the MAC layer frame isan Ethernet PON (EPON) or 10 gigabit EPON (10GEPON) message for a userdata channel that indicates the wavelength for the ONU, and wherein theEPON or 10GEPON message includes a broadcast logical link identifier(LLID) configured for upstream wavelength feedback.
 25. A methodimplemented at an optical line terminal (OLT) for a passive opticalnetwork (PON) comprising: sending, using a transmitter, a downstreamwavelength identification for an optical network unit (ONU) thatindicates a wavelength for the ONU in a Media Access Control (MAC) layerframe for an embedded channel, a control message channel, or a datachannel.
 26. The method of claim 25 further comprising: receiving, usinga receiver, an upstream wavelength feedback for the OLT that indicates awavelength for the ONU in a MAC layer frame for the same channel of thedownstream wavelength identification.
 27. The method of claim 25,wherein the indicated wavelength is a downstream wavelength transmittedfrom the OLT to the ONU, and wherein the wavelength is indicated to theONU in the MAC layer frame to configure the ONUs' receiver.
 28. Themethod of claim 25, wherein the indicated wavelength is an upstreamwavelength transmitted from the ONU to the OLT, and wherein thewavelength is indicated to the ONU in the MAC layer frames to configurethe ONUs' transmitter.
 29. The method of claim 25, wherein the indicatedwavelength is a downstream wavelength transmitted from the OLT to theONU, and wherein the wavelength is indicated to the ONU in the MAC layerframe to synchronize transmissions between the OLT and the ONU.
 30. Themethod of claim 25, wherein the indicated wavelength is an upstreamwavelength transmitted from the ONU to the OLT, and wherein thewavelength is indicated to the ONU in the MAC layer frame to synchronizetransmissions between the OLT and the ONU.
 31. The method of claim 25,wherein the MAC layer frame indicates the wavelength using a wavelengthidentifier (ID) that corresponds to the wavelength.
 32. The method ofclaim 25, wherein the MAC layer frame indicates the wavelength using anabsolute value for the wavelength.
 33. The method of claim 25, whereinthe MAC layer frame indicates the wavelength using a relative value forthe wavelength to a pre-determined absolute benchmark value.
 34. Amethod implemented at an optical network unit (ONU) for a passiveoptical network (PON) comprising: sending, using a transmitter, anupstream wavelength feedback for an optical line terminal (OLT) thatindicates a wavelength for the ONU in a Media Access Control (MAC) layerframe for an embedded channel, a control message channel, or a datachannel.
 35. The method of claim 34 further comprising: receiving, usinga receiver, a downstream wavelength identification for the ONU thatindicates a wavelength for the ONU in a MAC layer frame for the samechannel of the upstream wavelength feedback.
 36. The method of claim 34,wherein the indicated wavelength is a downstream wavelength transmittedfrom the OLT to the ONU, and wherein the wavelength is indicated in theMAC layer frame to confirm to the OLT the wavelength at the ONUs'receiver.
 37. The method of claim 34, wherein the indicated wavelengthis an upstream wavelength transmitted from the ONU to the OLT, andwherein the wavelength is indicated in the MAC layer frame to confirm tothe OLT the wavelength at the ONU's transmitter.
 38. The method of claim34, wherein the indicated wavelength is a downstream wavelengthtransmitted from the OLT to the ONU, and wherein the wavelength isindicated to the OLT in the MAC layer frame to synchronize transmissionsbetween the OLT and the ONU.
 39. The method of claim 34, wherein theindicated wavelength is an upstream wavelength transmitted from the ONUto the OLT, and wherein the wavelength is indicated to the OLT in theMAC layer frame to synchronize transmissions between the OLT and theONU.
 40. The method of claim 34, wherein the MAC layer frame indicatesthe wavelength using a wavelength identifier (ID) that corresponds tothe wavelength.
 41. The method of claim 34, wherein the MAC layer frameindicates the wavelength using an absolute value for the wavelength. 42.The method of claim 34, wherein the MAC layer frame indicates thewavelength using a relative value for the wavelength to a pre-determinedabsolute benchmark value.